Catalytic reactor and process for exothermic gas phase reactions

ABSTRACT

Disclosed is a reactor and process for exothermic vapour phase reaction, wherein the reactor ( 1; 101 ) comprises a pressure vessel ( 2; 102 ) having an inlet ( 3;103 ) for reactant(s) and an outlet ( 4; 104 ) for products; a plurality of beds ( 5; 105 ) with heterogeneous catalyst, each bed supported by a catalyst support grating ( 6; 106 ); a vapour collection chamber ( 9; 109 ) and a vapour redistribution chamber ( 10; 110 ) between successive pair(s) of beds for redistribution of vapourous reaction mixture over the inlet of the next bed; a diaphragm ( 11; 111 ) separating the vapour collection chamber ( 9; 109 ) from the vapour redistribution chamber; at least one pair of nested trough members extending at least partially across the diaphragm, each comprising an inner trough member ( 14; 114 ) having one or more apertures ( 18; 118 ), an outer trough ( 20; 120 ) having one or more apertures ( 21; 121 ) and a quench gas conduit ( 15; 115 ) provided with apertures ( 17; 117 ); the apertures ( 18; 118; 21; 121; 17; 117 ) arranged to provide a tortuous pathway for the flow of vapour and quench gas.

The present invention relates to a chemical reactor for use inequilibrium limited exothermic gas phase reactions, such as methanolsynthesis or ammonia synthesis and to a process for conductingexothermic vapour phase reactions.

The evolution of ammonia and methanol reactors from the 1960s to the1980s is outlined in a paper entitled “Review these developments inammonia and methanol reactors” by Umberto Zardi which was published inthe August 1982 edition of “Hydrocarbon Processing” at pages 129ff. Thefirst reactor described in this paper is the single bed Ammonia Casaleaxial reactor, designed for ammonia production, in which the synthesisgas flows under high pressure and temperature axially through a singlecatalyst bed mounted in a cylindrical reactor. Subsequent developmentsinclude the introduction of multi-bed designs and reactors utilisingradial as well as axial flow through the beds.

Thus, EP-A-0026057 describes an integrated process for the production ofammonia or methanol in which an appropriate synthesis gas is passedthrough a series of catalyst beds and, between each bed, the gas isquenched, by the injection of quench gas between the beds. Quenching thereaction mixture between catalyst beds helps to shift the equilibrium ofthe exothermic gas phase reaction(s) in a favourable direction and toalleviate the undesirable effects of the presence of pockets of vapourof elevated or reduced temperature. These effects include, in the caseof hot pockets, deterioration of catalyst and, in the case of coldpockets, possible snuffing of the reaction. Similarly, EP-A-0248284relates to a reactor for use in the production of ammonia, in which thereactor comprises a number of catalyst beds wherein cooler quench gas issupplied to the reactor between each bed. The purpose of this quench gasis the same as in EP-A-0026057, i.e. to shift the equilibrium of theexothermic gas phase reaction(s) in a favourable direction and toalleviate the undesirable effects of non-uniform temperaturedistribution within the catalyst beds.

The efforts of the prior art to counteract the problem of temperatureinhomogeneity in catalyst beds during equilibrium limited exothermic gasphase reactions have not been entirely successful and there is a need inthe art for a reactor design which will yield increased catalyst lifeand performance.

According to the present invention there is provided a reactor forconducting an exothermic vapour phase reaction comprising:

a) a pressure vessel having inlet means for supply of a gaseous reactantor reactants and outlet means for recovery of a product-containingstream therefrom;

b) a plurality of beds of a heterogeneous catalyst effective forcatalysis of the exothermic vapour phase reaction in the path of amaterial passing from the inlet means to the outlet means, each bedbeing supported within the pressure vessel by a respective supportmeans;

c) a vapour collection chamber and a vapour redistribution chamberbetween the or each successive pair of beds, the vapour collectionchamber being arranged to collect a vaporous reaction mixture from anexit end of one bed of the pair and the vapour redistribution chamberbeing arranged to redistribute vapour over the inlet end of the otherbed of the pair;

d) a diaphragm extending across the interior of the pressure vessel andseparating the vapour collection chamber from the vapour redistributionchamber;

e) at least one pair of nested trough members, the or each paircomprising an inner trough member and an outer trough member associatedwith the diaphragm and extending at least partially thereacross, theinner trough member and the outer trough member being nested so as todefine a space therebetween, the inner trough member opening to thevapour collection chamber and having one or more first apertures alongits length and the outer trough member communicating laterally on eachside with the vapour redistribution chamber by means of one or moresecond apertures opening laterally of the outer trough member along arespective side thereof, the space between the inner trough member andthe outer trough member providing a tortuous passageway for vapour fromthe vapour collection chamber to the vapour redistribution chamberthrough the at least one first aperture, through the space between theinner trough member and the outer trough member, and then through the atleast one second aperture to discharge laterally into the vapourredistribution chamber; and

f) a quench gas conduit associtated with the or each pair of troughmembers and being provided with one or more third apertures along itslength arranged to discharge quench gas into the vapour flowing alongthe tortuous pathway.

The pressure vessel may be of any size and shape but is preferablycircular in cross-section. Preferably the inlet means and the outletmeans are axially spaced one from another so that the overall directionof flow of reactants and products is from one end portion of the reactorto the other.

In one arrangement the beds of catalyst are substantially cylindrical.

The trough members may be of any suitable section provided that lateraldischarge of vapour into the vapour redistribution chamber is possible.A preferred form of trough member is arcuate in section. Preferably theangle subtended by the arc of an arcuate section trough member is fromabout 120° up to about 180°. Semi-circular section trough members may beused. Alternatively the trough members may be part-elliptical, forexample, semi-elliptical in section. If desired, the trough members maybe formed with one or more planar faces. For example, it is envisagedthat a trough member with a flat bottom and arcuate sides could be used,or a trough member with a flat bottom and inclined planar sides, whichmay be inclined, usually outwardly inclined to the bottom of the troughmember. The angle of inclination between the sides and the bottom of thetrough may be any suitable angle, for example from about 30° to about90°.

In one preferred arrangement the quench gas conduit associated with theor each respective pair of trough members is mounted at least partiallywithin the inner trough member of the pair.

The first and second apertures in the inner and outer trough membersrespectively may be of any suitable shape, e.g., circular, elliptical orrectangular, as may also be the third aperture or apertures in thequench gas conduit. The inner and/or outer trough members may each haveonly a single first or second aperture respectively, the aperture beingprovided in the form of an elongate slot. However, it will normally bepreferred for ease of construction to provide a plurality of aperturesalong the length of the respective trough member. Similarly, althoughthe quench gas conduit may have a single elongate slot to serve as thethird aperture, it will normally be preferred to provide a plurality ofthird apertures along the length of the conduit for ease of constructionand to enable the quench gas conduit to retain sufficient structuralstrength.

When the diaphragm and associated nested trough members are the onlymeans of vapour redistribution provided between successive catalyst bedsof the reactor it is preferred that the position of the second aperturesbe arranged such that the radial displacement, with respect to thenearest point on a reference axis lying in the plane of the diaphragmand also in a perpendicular plane bisecting the outer trough memberalong its longitudinal axis, of the second apertures from the plane ofthe diaphragm is not more than about 45°. However, this angle may begreater than 45° when further means of vapour redistribution areprovided between catalyst beds, as will be explained further below.

The second apparatus may be arranged in one or more rows on each side ofthe outer trough member so that the discharge of quenched reactionmixture to the vapour redistribution chamber is through a set of one ormore rows of second apertures on one side of the outer trough member andthrough a corresponding set of one or more rows of second apertures onthe other side thereof.

The reactor includes one or more quench gas conduits for supply ofquench gas which desirably segment the diaphragm in a symmetricalarrangement.

In a preferred arrangement the third aperture or apertures of the quenchgas conduit is or are aligned with the first aperture or apertures ofthe inner trough member. In this way the stream of quench gas from theconduit serves to draw vapour from the vapour collection chamber intothe space between the inner and outer trough members by means of aneductive effect created by the stream of quench gas issuing from thethird aperture or apertures of the quench gas conduit. In this way thequench gas and entrained vapour are turbulently mixed in passage alongthe tortuous pathway before passing on through the second apertures intothe vapour redistribution chamber.

As mentioned above, the quench gas conduit or conduits preferablysegment or partially segment the diaphragm in a symmetrical arrangement.Hence, if there is only one quench gas conduit this will normally extendsubstantially diametrically at least partially across the pressurevessel. If there are two or more quench gas conduits, then these mayextend at least partially along chords across the pressure vessel; inthis way substantially uniform mixing of the quench gas with the vapourflowing through the diaphragm and substantially uniform redistributionin the vapour redistribution chamber can be achieved.

Although the corresponding quench gas conduits of different diaphragmscan lie in common planes parallel to or including the axis of thepressure vessel, it is also envisaged that any given diaphragm may beradially offset about the axis of the pressure vessel relative to anadjacent diaphragm so that the quench gas conduit or conduits of onediaphragm is or are radially offset about the axis of the reactor withrespect to the corresponding conduit or conduits of at least one otherdiaphragm within the pressure vessel. Thus the angle of radialdisplacement about the axis of the pressure vessel of the quench gasconduits of one diaphragm relative to an adjacent diaphragm may rangefrom about 20° to about 90°, e.g. about 45° or about 60°. A preferredangle is 90°. Any practical number of catalyst beds may be employed inthe reactor of the invention. Preferably three or more beds are used.Moreover, there is no limit to the number of diaphragms or to the angleof offsetting about the axis of the pressure vessel of the quench gasconduit or conduits of one diaphragm relative to that or those of anadjacent diaphragm which may be envisaged.

In one embodiment of the invention, five catalyst beds are employed,with four diaphragms therebetween. However, it is also possible usingthe teachings of the invention to have two, three, four, six, seven,eight, nine or more catalyst beds in the reactor.

The radial offsetting of the quench gas conduits, and hence of theassociated trough members, of adjacent diaphragms is an importantpreferred feature of the invention because it helps to ensure thattemperature inhomogeneity across the cross-section of each catalyst bedis kept to a minimum. Thus, if after passage through a diaphragm, alocalised pocket of hot gas were present, this pocket would thenincrease in temperature even further relative to the whole stream onpassage through a subsequent catalyst bed. If the quench gas conduitsand trough member of successive diaphragms are aligned this increasesthe possibility that a local pocket of hot gas will prevail from onecatalyst bed to the next and so on until the outlet of the reactor isreached, causing premature deterioration of the catalyst and inefficientutilisation thereof. Respective radial offsetting of successivediaphragms decreases the likelihood of this occurring. Similarly, alocalised pocket of cold gas in a catalyst bed, which could causesnuffing of the reaction if allowed to prevail in a subsequent catalystbed of the reactor, is less likely to persist as a result of thispreferred feature of the invention.

The catalyst for use in methanol synthesis is preferably selected frombut is not limited to copper-containing catalysts, for example reducedCuO-ZnO catalysts. Preferred catalysts are those sold under thedesignation MK-101 by Haldor Topsøe A/S, Denmark and under thedesignation 51/3 by ICI Katalco.

For ammonia synthesis preferred catalysts include Fe impregnated withnon-reducible oxides of K, Ca, Al, Be, Ce, Si or mixtures thereof.

For methanol synthesis, the reaction vessel is preferably maintained ata pressure of between about 30 bar and about 100 bar, even morepreferably about 50 bar to about 80 bar. The reaction temperature isnormally between about 200° C. and about 300° C., for example betweenabout 250° C. and about 280° C.

For ammonia synthesis, the reaction vessel is typically maintained at apressure of up to about 600 bar. Pressures of between about 70 bar andabout 150 bar are preferred and a typical pressure is about 140 bar. Inammonia synthesis temperatures of between about 400° C. and about 550°C. are typically used.

It is desirable that the arrangement of diaphragm, trough members andapertures between adjacent catalyst beds shall not give rise to anundesirable pressure drop as the reaction mixture passes from the vapourcollection chamber to the vapour redistribution chamber. Hence thecross-section of the tortuous pathway should be of a size sufficient notto cause an excessive throttling of the flow of the reaction mixturethrough the reactor. In particular the respective numbers and sizes ofthe respective first, second and third apertures should be selected soas not to give rise to an unacceptable pressure drop across thediaphragm. It is within the competence of the person skilled in the artto calculate the pressure drops caused by particular geometricarrangements of quench gas conduits for any given set of number, sizeand arrangement of first, second or third apertures and to select anappropriate number and size of apertures in accordance with suchcalculations.

In one preferred embodiment of the invention, the reactor furthercomprises baffle means adjacent the diaphragm extending across theinterior of the pressure vessel and having at least one breach throughwhich the vaporous reaction mixture is constrained to pass. The bafflemeans may be located upstream or downstream of the diaphragm. More thanone baffle means may, if desired, be provided between any given pair ofcatalyst beds. In this case, baffle means may be provided both upstreamand downstream of the diaphragm. It is preferred that baffle means beprovided upstream of the diaphragm.

The purpose of the baffle means is to cause transverse mixing of thevaporous reaction mixture so that any temperature inhomogeneity in themixture entering a vapour collection chamber, if the baffle means isprovided upstream of the diaphragm, or a vapour redistribution chamber,if the baffle means is provided downstream of the diaphragm, iseliminated or reduced.

Thus, this arrangement has the additional advantage that if the reactionmixture passing into the vapour collection chamber or the vapourredistribution chamber between any given pair of catalyst beds has anon-homogenous temperature profile, its passage through the baffle meanscauses some homogenisation of this profile due to self-mixing of thereaction mixture as it passes through the at least one breach in thebaffle means.

The baffle means conveniently comprises a number of baffle plates whichare bolted or welded together to provide a substantially closed surfaceto the vaporous reaction mixture, negotiable only through the at leastone breach.

The at least one breach may comprise one or more grills forming part ofthe baffle means, each grill comprising a series of slots or aperturesin the baffle means. In this arrangement, it is important that thebaffle means in the region of the slots or apertures be of a thicknesssufficient to create a tunnelling effect as a vaporous reaction mixturepasses therethrough causing a degree of homogenisation of the reactionmixture to occur as it passes through the slots or apertures.

If the baffle means is of circular cross section, a single grilltraversing the baffle means diametrically may be provided. Alternativelya plurality of symmetrically arranged grills may be provided. These may,for example when the reactor is of circular transverse cross section,lie along chords of the baffle means. Alternatively, grills may bearranged at various points of the baffle means. It will be understood bythose skilled in the art that the purpose of these grills is at leastpartially to homogenise the vaporous reaction mixture as it passesthrough the baffle means. Accordingly, there is a multitude of possiblearrangements of a grill or grills which would achieve this aim. Theexamples given above are not intended to be exhaustive and it is notnecessary to describe in detail every one of these arrangements sincethe skilled person will understand the likely efficacy of any particulararrangement.

As the intercepted vaporous reaction mixture meets the closed surfaceprovided by the baffle means, it is deflected and flows over the closedsurface of the baffle means until it encounters the breach. The impactof the vaporous mixture upon the surface causes turbulent mixing of themixture. This homogenises the mixture to some extent and helps preventthe formation or persistence of localised pockets of hot or cold gas inthe reaction mixture. It is desirable to avoid the formation of hotpockets of gas because of the deleterious effect such pockets may haveon the performance and life of the heterogeneous catalyst in the nextsuccessive catalyst beds. Cold pockets are also undesirable because theymay snuff the reaction.

The reaction mixture can negotiate the baffle means only by flowingthrough the breach towards the inlet end of the next successive catalystbed. This promotes transverse mixing of the vaporous reaction mixtureflowing towards and through the breach from different directions.

In another preferred embodiment of the invention, there is provided abarrier means in association with the at least one breach of the bafflemeans. The efficacy of the process in which the reaction mixture ishomogenised to some extent on passing through the breach is improved bythe provision of such barrier means associated with the or each breach.The barrier means may be provided above or below the baffle means, orboth above and below the baffle means. The barrier means has theimportant and advantageous effect of promoting turbulent mixing of thevaporous reaction mixture as it negotiates the baffle means. Vaporousreaction mixture flowing transversely across the baffle means andthrough the breach encounters the barrier means and is prevented therebyfrom flowing through the breach without substantially altering itstransverse direction of flow.

The barrier means preferably comprises a deflection surface standing outfrom the plane of the baffle means, providing a barrier to transverseflow of the vaporous reaction mixture.

There are many arrangements of barrier means which may be envisaged bythe skilled person to promote turbulent mixing of the vaporous reactionmixture. The following embodiments are not therefore intended to beexhaustive. One embodiment of barrier means comprises a walled memberhaving an opening at one end thereof to allow ingress of a vaporousreaction mixture. The walled member may comprise three planar wallsurfaces joined at right angles to each other to form three sides of arectangular pen. This type of barrier means is arranged so that itstraddles the at least one breach. The breach may comprise an open gapin the baffle means. Alternatively, it may comprises a grill asdescribed above. A vaporous reaction mixture entering the pen at itsopen end is subjected to turbulent mixing around the walls thereof. Thismixing occurs before or after passing through the breach, depending onwhether the pen is situated above or below the breach. Both arrangementsare possible.

The pen may, if desired, be provided with a cover so that vapour canonly enter or escape the pen via its open end or via the diaphragmbreach.

Accordingly one preferred embodiment of the invention utilises a bafflemeans formed from a baffle plate, or a number of baffle plates, in whicha grill forms the at least one breach and the barrier means comprises anopen-ended three-walled pen arranged over or under the grill and securedto the baffle plate or plates, for example by means of bolts, rivets ora weld.

In one preferred embodiment of the invention, a plurality of open-ended,three-walled pens are arranged along the length of the breach, each penhaving its open end oriented at 180° to its neighbour or neighbours. Inthis way, a vaporous reaction mixture flowing across the closed surfaceof the baffle means encounters a turbulent mixing zone within a pen,regardless of its original direction of flow.

If a series of barrier means is provided, it may be preferred to sealany gaps between neighbouring barrier means to prevent the vaporousreaction mixture from flowing therethrough.

In another embodiment of the invention, the barrier means is formed as araised wall running along and adjacent the length of the breach, thewall having a series of slots or apertures along its length to allowpassage of a vaporous reaction mixture therethrough. Preferably, twoparallel walls, one on either side of the breach, are provided. In thisarrangement, the slots or apertures in each wall may be linearly offsetwith respect to each other. Thus, a vaporous reaction mixture flowingacross the closed surface of the baffle means and through an aperture inone wall of a pair towards the other wall of the pair encounters aclosed surface on the other wall. Impact of the vapour upon this closedsurface facilitates turbulent mixing of the vaporous reaction mixtureflowing between the walls.

The wall or walls may be provided either above or below the bafflemeans, or both above and below the baffle means.

In another embodiment of the invention, the barrier means is provided inthe following manner. The baffle means is originally formed without abreach. A slot with a linear axis and castellated plan is cut in thebaffle means to provide a series of interleaving fingers. These fingersmay then be bent upwardly, or downwardly, out of the plane of the bafflemeans to provide a series of raised, or lowered, interleaving fingers.In this case, the breach is provided by the slot cut in the baffle meansand the barrier means is provided by the fingers outstanding from theplane of the baffle means. It is also possible to provide matingcastellated edges on a pair of baffle plates which can then be joined inthe plane of each baffle plate to obtain this type of baffle means.

The invention further provides a continuous process for conducting anexothermic vapour phase reaction, which process comprises:

a) supplying to a pressure vessel via inlet means therefor a gaseousreactant or reactants;

b) maintaining in the pressure vessel temperature and pressureconditions effective for production of a desired product by means of theexothermic vapour phase reaction;

c) allowing the gaseous reactant or reactants to flow in turn through aplurality of beds of a heterogeneous catalyst effective for catalysis ofthe exothermic vapour phase reaction, each bed being supported withinthe pressure vessel by a respective support means;

d) collecting vaporous reaction mixture exiting a first bed of eachsuccessive pair of beds in a vapour collection chamber which isseparated from a corresponding downstream vapour redistribution chamberfor redistributing vapour over the inlet end of the other bed of therespective pair by a diaphragm extending across the interior of thepressure vessel and separating the vapour collection chamber from thevapour redistribution chamber;

e) allowing vaporous reaction mixture to pass from the vapour collectionchamber to the vapour redistribution chamber by means of a tortuouspassageway formed by at least one pair of nested trough memberscomprising an inner trough member and an outer trough member associatedwith and extending at least partially across the diaphragm, the innertrough member opening to the vapour collection chamber and having one ormore first apertures along the length of the inner trough member and theouter trough member communicating laterally on each side with the vapourredistribution chamber by means of one or more second apertures openinglaterally of the outer trough member along a respective side thereof,the space between the inner trough member and the outer trough memberproviding said tortuous passageway for vapour from the vapour collectionchamber to the vapour redistribution chamber through the at least onefirst aperture, through the space between the inner trough member andthe outer trough member, and then through the at least one secondaperture to discharge laterally into the vapour redistribution chamber;

f) supplying quench gas to the vaporous reaction mixture passing throughthe diaphragm by means of a quench gas conduit associated with each pairof trough members, the quench gas conduit being provided with one ormore third apertures along its length arranged to discharge quench gasinto the vapour flowing along the tortuous pathway; and

g) recovering from the pressure vessel via outlet means provideddownstream from the final catalyst bed a vaporous product streamcontaining said product.

In a preferred process according to the invention there is furtherincluded the step of providing, adjacent the diaphragm, baffle meansextending across the interior of the pressure vessel and having at leastone breach therethrough, and constraining the vaporous reaction mixtureto pass through the baffle means.

In order that the invention may be clearly understood and fully carriedinto effect, a number of embodiments thereof will now be moreparticularly described with reference to the accompanying drawings, inwhich:

FIG. 1 is a simplified vertical cross-sectional diagram of a reactordesigned in accordance with the present invention;

FIG. 2 is a horizontal cross-section on line A—A or C—C of FIG. 1;

FIG. 3 is a cross section on lines E—E or F—F of FIG. 2 or on line G—Gor H—H of FIG. 4;

FIG. 4 is a horizontal cross-section through a second form of reactor,corresponding to a cross-section on line B—B or D—D of FIG. 1;

FIG. 5 is an expanded vertical cross-section view of part of the reactorshown in FIG. 1;

FIG. 6 is a simplified vertical cross-sectional diagram of a third formof reactor designed in accordance with the present invention;

FIGS. 7, 7 a, 8, 8 a, 9, 10, 10 a and 11 are partial and schematic crosssections on line I—I of FIG. 6, or of modified forms of the reactorshown in FIG. 6;

FIG. 12 is a partial and schematic perspective of a single barrier meansand breach of the baffle means of FIGS. 10 and 11;

FIGS. 13, 13 a, 13 b, 14, 15, 16 and 16 a are partial and schematiccross sections on line I—I of modified forms of the reactor shown inFIG. 6;

FIG. 17 is a partial and schematic perspective of the barrier means andbreach of the baffle means of FIGS. 16 and 16a; and

FIG. 18 is an enlarged vertical cross sectional diagram through a partof the reactor of FIG. 6.

For the avoidance of doubt, FIGS. 1 to 18 are intended only as an aid tounderstanding the invention and are not to be construed as limiting thescope of the invention with regard to the precise number of catalystbeds or positioning thereof, the shape of the reactor vessel or any ofits ancillary features, the precise shape or positioning of the quenchgas conduits, trough members, apertures and diaphragms, other than thoseaspects of shape and position which are described more particularlybelow, or any other feature of the reactor which is not expresslyclaimed below.

Referring to FIG. 1, reactor 1 comprises an outer pressure shell 2provided with a top inlet 3 for incoming synthesis gas or vapour and abottom outlet 4 for a vaporous product stream. Reactor 1 is providedwith five beds 5 of a heterogeneous methanol synthesis catalyst, eachbed being supported by a respective catalyst support grating 6.

A number of parallel catalyst support beams 7 project upwardly into eachbed 5 to provide lateral support for the catalyst grating 6 and for thecatalyst of bed 5. For clarity, support beams 7 are shown only onbottommost grating 6 in FIG. 1. Reference numeral 8 indicates a manholethrough which catalyst may be loaded into and unloaded from reactor 1.Below each catalyst bed 5 other than the bottommost one is a vapourcollection chamber 9, whilst above each catalyst bed 5 other than thetopmost one is a vapour redistribution chamber 10. Each vapourcollection chamber 9 is divided from its adjoining vapour redistributionchamber 10 by a diaphragm 11.

Referring to FIG. 2, it can be seen that diaphragm 11 comprises a numberof baffle plates 12 which prevent the passage of gas from vapourcollection chamber 9 to vapour redistribution chamber 10 (FIG. 1) exceptthrough open channels 13 defined by troughs 14 and conduits 15. Conduits15 extend along chords of diaphragm 11 so as to divide it into segmentsand carry quench gas from inlet pipes 16. As can be seen from FIG. 2each inlet pipe 16 and its conduit 15 form a T-shape. Conduits 15 aresymmetrically arranged with respect to a central axial plane of reactor1. Any number of conduits 15 can be employed in the reactor of theinvention but, if an odd number is to be used, then one of the conduits15 should preferably occupy a line bisecting diaphragm 11.

The quench gas supplied via conduit 15 may be an inert gas but is moreusually fresh or recycled synthesis gas or a mixture thereof. It is at alower temperature than the gas exiting catalyst bed 5 above therespective diaphragm 11. Typically it is at least about 100° C., up toabout 200° C. or more, cooler than that exist gas temperature. (If areactor of similar design is used in the synthesis of ammonia, thequench gas temperature is desirably about 200° C. to about 400° C. lowerthan the temperature of the reaction mixture collected in the vapourcollection zone.) The purpose of introducing such quench gas is toprovide a temperature quench thereby lowering the average temperature ofthe vapour recovered from an upstream catalyst bed 5 (FIG. 1), thetemperature of the vapour having been raised in passage through bed 5 bythe exothermic reaction of synthesis gas. The temperature quench thusachieved between successive catalyst beds 5 serves to adjust the inlettemperature conditions to the next bed 5 away from the equilibriumtemperature. This allows the product forming reactions to predominate asthe reaction mixture passes on into the next bed. The quench gas mustaccordingly be supplied in conduits 15 at a lower temperature than thatof the vapour entering troughs 14 from respective vapour collectionchamber 9 (FIG. 1).

Conduits 15 have a series of axial slots or holes 17 (FIG. 3) on theirlowermost surfaces, which slots or holes permit egress of quench gasinto troughs 14. Troughs 14 are provided with a series of axial slots orholes 18 (FIG. 3) which are substantially co-radial with slots or holes17 to allow direct passage of quench gas from conduits 15 into mixingzones 19 (FIG. 3) situated in the respective radial spaces definedbetween troughs 14 and lower co-axial troughs 20.

Hot vapour recovered from catalyst bed 5 (FIG. 1) flows into therespective vapour collection chamber 9 (FIG. 1) and into respective openchannels 13 between troughs 14 and conduits 15. The hot vapour inchannels 13 becomes entrained in the flow of quench gas from slots orholes 17 and passes through slots or holes 18 (FIG. 3) into mixing zones19. Troughs 20 are provided with a series of axial slots or holes 21(FIG. 3) to allow egress of a temperature-quenched gas stream into thevapour redistribution chamber 10 (FIG. 1). However, slots or holes 21are not radially aligned with slots or holes 17 and 18 but are radiallyoffset with respect thereto so that the quench gas and entrained hotvapour stream entering mixing zones 19 are directed at respective closedsurfaces on troughs 20, on which the gas stream impacts, causingturbulent mixing of the quench gas with the vapour within mixing zones19. The mixed gas stream exits laterally into vapour redistributionchamber 10 (FIG. 1) via slots or holes 21 which are symmetricallydisposed with respect to the axis of each trough 20. Moreover the gasstream is constrained to follow a tortuous pathway from entering intochannels 13, through holes or slots 18, then through mixing zones 19 andout through holes or slots 21. The symmetrical disposition of slots orholes 21 is important because it ensures that the mixed gas stream isevenly distributed into vapour redistribution chamber 10 (FIG. 1).Uneven distribution of the vapour may lead to uneven reaction throughthe next catalyst bed 5, giving rise to inefficient utilisation of thecatalyst and to premature catalyst deterioration due to hot-spotformation or to snuffing of the reaction through cold spot formation.

Quenched methanol-containing vapour stream passes into vapourredistribution chamber 10 and into a further catalyst bed 5. Uponrecovery from this further catalyst bed 5, the hot methanol-containingvapour stream is once again quenched in passage from a further vapourcollection chamber 9 to a further vapour redistribution chamber 10through a quenching system similar to that described above.

The quench gas conduits 15 of axially successive diaphragms 11 arepreferably radially offset with respect to each other about the verticalaxis of reactor 1. Thus, the topmost and third from top diaphragms 11and associated quench gas conduits 15 in FIG. 1 are orientatedidentically to each other but quench gas conduits 15 of the second andfourth diaphragms 11 (from the top of reactor 1) are radially offset by90° about the vertical axis of reactor 1 with respect to quench gasconduits 15 of the topmost and third from top diaphragms 11.

FIG. 4 is a horizontal cross section through a modified form of reactoron a line corresponding to line B—B or D—D of FIG. 1, The reactor ofFIG. 4 differs from that of FIG. 2 in that, instead of quench gas inletpipes 16 being joined to conduits 15 at a T-joint, they are in line withconduits 15.

Baffle plates 12 are shown in FIG. 4 forming diaphragm 11 which dividesvapour collection chamber 9 from vapour redistribution chamber 10 (FIG.1). Hot vapour from vapour collection chamber 9 enters troughs 14 andbecomes entrained in the downward flow of quench gas emerging fromconduits 15. Quench gas is supplied via inlet pipes 16. The quench gassparging and mixing in the reactor of FIG. 4 occurs in a substantiallyidentical manner to that occurring in the reactor of FIG. 2.

The radial offsetting of successive quench gas conduits 15 relative toeach other about the vertical axis of reactor 1 has the additionaladvantage that any temperature inhomogeneity in the quenched gas streamrecovered from a catalyst bed 5 is not perpetuated by subsequent mixingthrough the subsequent catalyst bed 5. This feature thereforesubstantially eliminates the persistent development of hot or cold spotsin a downstream bed 5 as a result of local hot or cold spot formation inan upstream bed 5.

The radial offsetting of successive quench gas conduits 15 is perhapsbest illustrated in FIG. 5 which shows a cross-sectional view of part ofthe reactor of FIG. 4 (that is the reactor of FIG. 1 with colinearquench gas conduits 15 and inlet pipes 16). Hot vapor is recovered fromcatalyst bed 5 in vapour collection chamber 9 and flows into openchannels 13 (FIG. 3) bounded by conduits 15 and troughs 14 (FIG. 3).Quench gas is supplied in conduits 15 via inlet pipes 16. The hot vapourfrom the vapour collection chamber 9 flows via channels 13 into troughs14 and becomes entrained in the stream of quench gas flowing fromconduits 15 through slots 17 and 18 (FIG. 3). The hot vapour istherefore carried into mixing zones 19 by an eductive effect. Thequenched gas stream exits from troughs 20, after turbulent mixing,laterally through slots 21 which are arranged in two rows on each sideof troughs 20. The two rows of slots 21 are symmetrically arranged ineach trough 20 with respect to the vertical plane of symmetry throughslots 17 and 18. The symmetrical arrangement of slots 21 ensureshomogeneous distribution of the quenched gas stream into the vapourdistribution chamber 10. It also ensures that the entrained gas streamsentering trough 20 via slots 18 are mixed equally irrespective of thedirection in which they impact upon the closed wall of trough 20. Thequenched gas passes on through bed 5′ and the resulting reaction mixtureis then similarly mixed with quench gas in passage through diaphragm11′. Conduits 15′ and troughs 14′ and 20′ are radially offset by anangle of 90° about the vertical axis of the reactor with respect toconduits 15 and troughs 14 and 20 respectively. Mixing takes place inthe same way as described above. However, due to the redistribution ofgas that occurs in passage from vapour collection chamber 9 along thetortuous pathway to holes or slots 21, a local pocket of hot or cold gasfollowing the route indicated by line S on FIG. 5 would not persist incatalyst bed 5″, as might be the case if the conduits 15′ and troughs14′ and 20′ were respectively aligned in a vertical plane with conduits15 and troughs 14 and 20.

In FIG. 5 the angle of radial offset between conduits 15 and 15′ aboutthe vertical axis of the reactor is 90°. It is alternatively possible toutilise a smaller angle of offset, e.g. 45° or 60 °, between conduits 15and 15′.

One advantage of the invention is that any pressure drop occurring onpassage of the synthesis gas mixture through diaphragm 11 can be atleast partially restored by supplying quench gas in conduit 15 in amanner and at a pressure sufficient to increase the momentum of the gasmixture flowing along the tortuous passageway.

Referring now to FIG. 6, there is shown a second embodiment of theinvention, in which reactor 101, pressure shell 102, top inlet 103,bottom outlet 104, catalyst beds 105, support gratings 106, supportbeams 107 and manhole 108 are arranged substantially identically toitems 1 to 8 of the reaction 1 shown in FIG. 1.

Between successive catalyst beds 105, of which there are four in reactor101, is a vapour collection chamber 109 and a vapour redistributionchamber 110. Vapour collection chamber 109 is separated from vapourredistribution chamber 110 by diaphragm 111. Baffle means 122 is shownmounted within vapour collection chamber 109. However, it is alsopossible to mount baffle means 122 within vapour redistribution chamber110. Pressure vessel 102 is substantially circular in cross section andtwo quench gas conduits 115 lie along parallel chords of diaphragm 111.

FIG. 7 shows half of a cross section on line I—I of FIG. 6. Baffle means122 is of circular cross section and is provided along its diameter witha breach 123 comprising a grill 124. Reference numeral 125 in FIG. 7represents in outline the presence of a quench gas conduit 115 andassociated nested trough members beneath baffle means 122. Quench gasconduit 115 is one of a pair of such conduits, the other conduit of thepair lying along a chord of diaphragm 111 parallel and symmetricallyarranged with respect to the conduit shown as reference numeral 125.FIG. 7a shows another cross section on the whole of baffle means 122 andbreach 123.

Referring to FIG. 7, breach 123 comprises a series of parallellongitudinal slotted apertures forming a grill 124, in baffle means 122.

Although grill 124 shown in FIG. 7 comprises a series of parallel slots,it will be apparent to the skilled person that a number of alternativearrangements can be envisaged. For example, grill 124 may comprise asymmetric array of circular holes, or may be formed as a mesh structure,for example resembling chicken wire.

FIGS. 8 to 17 show alternative arrangements of baffle means 11. In FIG.8 baffle means 122 has two grills 124 arranged on parallel chords ofbaffle means 122. FIG. 8a shows another cross section on baffle means122.

In FIG. 9, a plurality of grills 124 are shown in a spaced apartarrangement on baffle means 122. Many other such arrangements can beenvisaged by those skilled in the art.

FIG. 10 shows baffle means 122 and breach 123 which is simply an opengap in baffle means 122. No grill is present. Breach 123 is overlaidwith a series of barrier means 126. Barrier means 126 is a pen mountedon baffle means 122. Each pen 126 has a lid 126 a, which is shown inFIG. 10a, an end wall 127 and two side walls 128.

FIG. 11 shows an alternative embodiment of the pen arrangement shown inFIG. 10, in which the barrier means 126 b is a pen having an end wall127 and side walls 128. However, no lid is provided. In the embodimentof FIG. 11, the gaps between neighbouring pens 126 b have been sealed toprevent the flow of vaporous reaction mixture therebetween. Vaporousreaction mixture cannot thereby flow across the closed surface of bafflemeans 122 without impacting upon an upstanding wall 127 or 128. An eventwhich causes turbulent mixing of the vaporous reaction mixture stream.

FIG. 12 shows, in perspective, a detail of a modified version of thebaffle means of FIG. 11. In the embodiment of FIG. 12, the baffle meansis breached by a diagonally slotted grill 124 and is overlaid by aseries of barrier means 126 b, only one of which is shown in FIG. 12.

In FIGS. 10, 10 a, 11 and 12, pens 126 are shown as open-endedrectangular enclosures into which vaporous reaction mixture may flow andbecome turbulently mixed by impaction against one or more of upstandingwalls 127 and 128 and, if present, lid 126 a, before passing throughbaffle means 122 via breach 123 or 124. Many other arrangements ofopen-ended enclosures may be envisaged by those skilled in the art. Forexample, a single wall upstanding from baffle means 122 and runningalong the length of breach 123 may be provided, the wall being wavy incross section along the length of the breach. Alternatively, individualopen-ended enclosures 16 may be formed with arcuate, semi-circular orpart-elliptical cross section. Combinations of planar and arcuateupstanding walls 127 and 128 may be envisaged. For example, open-endedenclosure 126 may comprise a planar end wall 127 and curviform sidewalls 128, or a curviform end wall 127 and planar side walls 128. V-planenclosures may be used, as may open-ended pentagonal, hexagonal,heptagonal, octagonal or other plan enclosures.

FIGS. 13, 13 a, 13 b, 14 and 15 show alternative forms of barrier meanson baffle means 122. FIGS. 13, 14 and 15 show baffle means 122 in topplan view (only half of baffle means 122 is shown). In addition, FIGS.13a and 13 b show two alternative embodiments of the invention in a sideelevation (the whole of baffle means 122 being shown). Baffle means 122is provided with a breach 123 along its diameter. Breach 123 may containa grill or mesh structure but is simply an open gap in baffle means 122in the embodiment shown in these Figures. On either side of breach 123,baffle means 122 is provided with a pair of parallel walls 129. In FIG.13a the walls are upstanding from the surface of baffle means 122. InFIG. 13b the walls are protrude downwardly from the surface of bafflemeans 122.

Referring to FIGS. 13, 13 a and 13 b, each wall 129 is provided, atregularly spaced intervals along its length, with a series of apertures,or doorways, 130 which permit a vaporous reaction mixture flowingtransversely across the closed surface of baffle means 122 to passthrough respective wall 129 and into the space defined between walls 129above breach 123.

In the embodiment of FIG. 13, the doorways 130 of one wall 129 of a pairof parallel walls 129 are offset linearly with respect to thecorresponding doorways 130′ of the other wall 129′ of the pair. Thus, avaporous reaction mixture flowing through one doorway 130 in one wall129 of the pair impacts against the closed surface of the other wall129′ of the pair and is thus turbulently mixed before passing throughbreach 123. The size of individual doorways 130, 130′, the spacingbetween doorways 130, 130′ and the magnitude of linear offset betweenopposing sets of doorways 130, 130′ may be determined by the skilledperson using a scale model or computional fluid dynamics. FIGS. 13, 14and 15 illustrate to some extent the range of possible variation. FIGS.13 and 14 are identical, FIG. 14 indicating, by arrows a and brespectively, the width of an individual doorway 130 and the magnitudeof linear offset of one particular embodiment of the invention. Thewidth (a) of a single doorway 130 is preferably between one hundredthand one tenth of the diameter of baffle means 122. The magnitude (b) oflinear offset between opposing doorways is preferably between one halfof and twice width (a).

However, other embodiments of the invention may be provided in whichdoors 130 of opposing walls 129 are not offset with respect to eachother. Such an embodiment is shown in FIG. 15.

FIGS. 16, 16 a and 17 show another alternative arrangement of barriermeans. Baffle means 122 (only half of which is shown in the top planview of FIG. 16) is provided with a slot 131 of castellated plan whichforms the breach in baffle means 122. Castellated slot 131 correspondsto a series of interleaving fingers 132 in baffle means 122. Wheninterleaving fingers 132 are bent out of the plane of baffle means 122,as is shown in FIGS. 16a and 17, an effective barrier means is provided.Vaporous reaction mixture flowing through slot 131 impacts upon theinterleaved structure formed by fingers 132 and becomes turbulentlymixed as a result. In FIG. 16 reference letters c and d indicaterespectively the width of each open-ended rectangular enclosure of slot131 and the width of each interlocking finger 132 created thereby.Preferably, width (c) is between one thousandth and one fifteenth of thediameter of baffle means 122. Preferably, the width (d) of eachinterlocking finger is between one hundredth and one tenth of thediameter of baffle means 122. Reference letter e indicates the length ofeach finger 132, which is preferably between one fiftieth and one fifthof the diameter of baffle means 122, and α indicates the preferred anglebetween fingers 132 and the plane of baffle means 122. Preferably, α isbetween 20° and 70°.

Returning to FIG. 6, hot vapour recovered from catalyst bed 105 flowsinto the respective vapour collection chamber 109 and, after deflectionagainst the closed surface of baffle means 122, is channelled throughbreach 123. Baffle means 122 is provided on its upper surface,immediately above breach 123 with barrier means 126. Barrier means 126is a series of open-ended rectangular walled enclosures of the typedescribed above with reference to FIGS. 10 to 12. These help to deflecthot vapour flowing across the surface of baffle means 122 through breach123 and also act as an impaction surface of or surfaces for turbulentmixing of the vapour. The tendency for formation of localised pockets ofhot or cold vapour is thereby reduced. After passing through bafflemeans 122 in this way, the hot vapour stream continues on in vapourcollection chamber 109 until it meets diaphragm 111.

Quenched methanol-containing vapour stream passes into vapourredistribution chamber 110 and into a further catalyst bed 105. Uponrecovery from this further catalyst bed 105, the hot methanol-containingvapour stream is once again quenched in passage from a further vapourcollection chamber 109 to a further vapour redistribution chamber 110through a quenching system similar to that described above.

In the reactor of FIG. 6, diaphragm 111 and associated baffle means 122are arranged in such a way that the longitudinal axis of breach 123 inbaffle means 122 is at 90° to the longitudinal axis of each quench gasconduit 115 of diaphragm 111. This is a preferred arrangement whichfacilitates homogenisation of the hot vapour flowing through vapourcollection chamber 109. However, it is also possible to arrangediaphragm 111 and baffle means 122 in other ways. For example, thelongitudinal axis of series of breaches 123 could be arranged parallelto that of quench gas conduits 115 or could be radially offset withrespect thereto by some other angle, for example 30°, 45° or 60°.

In the reactor of FIG. 6, the quench gas conduits 115 of axiallysuccessive diaphragms 111 are radially offset with respect to each otherabout the vertical axis of reactor 105. Thus, the topmost and lowermostdiaphragms 111 and associated quench gas conduits 115 in FIG. 6 areorientated identically to each other but quench gas conduits 115 ofintermediate diaphragm 111 are radially offset by 90° about the verticalaxis of reactor 101 with respect to quench gas conduits 115 of thetopmost and lowermost diaphragms 111. Consequently, intermediate bafflemeans 122 is also offset by 90° with respect to topmost and bottommostbaffle means 122. However, it is also possible to arrange successivequench gas conduits 115 in parallel alignment with each other. Theprovision of baffle means 122 and associated breach 123 reduces thepossibility that localised pockets of hot or cold gas will persistthrough the reactor in passage through a series of diaphragms 111arranged with quench gas conduits 115 in parallel.

The radial offsetting of successive quench gas conduits 115 is perhapsbest illustrated in FIG. 18 which shows a vertical cross-section throughpart of a modified form of the reactor of FIG. 6 (in which quench gasconduits 115 and inlet pipes 126 are colinear). Hot vapour is recoveredfrom catalyst bed 105 in vapour collection chamber 109 and flows throughbreach 123 in baffle means 122 after turbulent impaction against theclosed surface of baffle means 122 and barrier means 126. The vapourthen flows into open channels 113 (FIG. 3) bounded by conduits 115 andtroughs 114 (FIG. 3). Quench gas is supplied in conduits 115 via inletpipes 126. The hot vapour from the vapour collection chamber 110 flowsvia channels 113 into troughs 114 and becomes entrained in the stream ofquench gas flowing from conduits 115 through slots 117 and 118 (FIG. 3).The hot vapour is therefore carried into mixing zones 119 by an eductiveeffect. The quenched gas stream exits from troughs 120, after turbulentmixing, laterally through slots 121 which are arranged in two rows oneach side of troughs 120. The two rows of slots 121 are symmetricallyarranged in each trough 120 with respect to the vertical plane ofsummetry through slots 117 and 118. The symmetrical arrangement of slots121 ensures homogeneous distribution of the quenched gas stream into thevapour distribution chamber 110. It also ensures that the entrained gasstreams entering trough 120 via slots 118 are mixed substantiallyequally irrespective of the direction in which they impact upon theclosed wall of trough 120. The quenched gas passes on through bed 105′and the resulting reaction mixture is then similarly mixed with quenchgas in passage through diaphragm 111′. Conduits 115′ and troughs 114′and 120′ are radially offset by an angle of 90° about the vertical axisof the reactor with respect to conduits 115 and troughs 114 and 120respectively. Mixing takes place in the same way as described above.

What is claimed is:
 1. A reactor for conducting an exothermic vapourphase reaction comprising: a) a pressure vessel having inlet means forsupply of a gaseous reactant or reactants and outlet means for recoveryof a product-containing stream therefore; b) a plurality of beds of aheterogeneous catalyst effective for catalysis of the exothermic vapourphase reaction in the path of a material passing from the inlet means tothe outlet means, each bed being supported within the pressure vessel bya respective support means; c) a vapour collection chamber and a vapourredistribution chamber between the or each successive pair of beds, thevapour collection chamber being disposed adjacent an exit end of one bedof the pair and arranged to collect a vaporous reaction mixture from theexit end of said one bed of the pair and the vapour redistributionchamber being disposed adjacent an inlet end of the other bed of thepair and arranged to redistribute vapour over the inlet end of saidother bed of the pair; d) a diaphragm extending across the interior ofthe pressure vessel and separating the vapour collection chamber fromthe vapour redistribution chamber for preventing flow of vapour from thevapour collection chamber to the vapour redistribution chamber; e) atleast one pair of nested trough members, the or each pair comprising aninner trough member and an outer trough member associated with thediaphragm and extending at least partially thereacross, the inner troughmember and the outer trough member being nested so as to define a spacetherebetween, the inner trough member opening to the vapour collectionchamber and having one or more first apertures along its length and theouter trough member communicating laterally on each side with the vapourredistribution chamber by means of one or more second apertures openinglaterally of the outer trough member along a respective side thereofinto the vapour redistribution chamber, the space between the innertrough member and the outer trough member providing a tortuouspassageway for vapour from the vapour collection chamber to the vapourredistribution chamber through the at least one first aperture, throughthe space between the inner trough member and the outer trough member,and then trough the at least one second aperture to discharge laterallyinto the vapour redistribution chamber; and f) a quench gas conduitassociated with the or each pair of trough members and being providedwith one or more third apertures along its length arranged to dischargequench gas into the vapour flowing along the tortuous pathway, wherebythe diaphragm prevents passage of vapour from the vapour collectionchamber to the vapour redistribution chamber and whereby vapour passesfrom the vapour collection chamber to the vapour redistribution chamberthrough the tortuous passageway and is admixed with quench gas inpassage through the tortuous passageway.
 2. A reactor according to claim1, wherein the reactor further comprises baffle means adjacent thediaphragm extending across the interior of the pressure vessel andhaving at least one breach through which the vaporous reaction mixtureis constrained to pass.
 3. A reactor according to claim 2, wherein thebreach comprises one or more grills forming part of the baffle means. 4.A reactor according to claim 2, wherein there is provided in associationwith the breach a barrier means comprising a deflection surfaceoutstanding from the plane of the baffle means.
 5. A reactor accordingto claim 4, wherein the barrier means comprises upstanding wall meansdefining a plurality of penned enclosures arranged along the length ofthe breach.
 6. A reactor according to claim 4, wherein the barrier meanscomprises a wall running along the length of the breach and standing outfrom the surface of the baffle means, the wall having a series of slotsor apertures along its length to allow the passage of a vaporousreaction mixture therethrough.
 7. A reactor according to claim 6,wherein two parallel walls are provided, wherein one wall is provided onone side of the breach and another wall is provided on the opposite sideof the breach.
 8. A reactor according to claim 7, wherein the slots orapertures in one wall are linearly offset with respect to the otherparallel wall.
 9. A reactor according to claim 4, wherein the barriermeans comprises a series of interleaved fingers outstanding from theplane of the baffle means.
 10. A reactor according to claim 1, whereinthe heterogeneous catalyst is a methanol synthesis catalyst.
 11. Areactor according to claim 10, wherein the catalyst is acopper-containing catalyst.
 12. A reactor according to claim 1, whereinthe heterogeneous catalyst is an ammonia synthesis catalyst.
 13. Areactor according to claim 12, wherein the ammonia synthesis catalyst isselected from Fe impregnated with at least one non-reducible oxide of ametal selected from K, Ca, Al, Be, Ce, Si and mixtures of two or morethereof.
 14. A reactor according to claim 1, wherein the or each saidquench gas conduit segments or segment the diaphragm in a symmetricalarrangement.
 15. A reactor according to claim 1, wherein the inner andouter trough members are arcuate in section.
 16. A reactor according toclaim 1, wherein the second apertures are arranged in two sets each ofone or more rows, one set being arranged to discharge vapour laterallyto the vapour redistribution chamber on one side of the outer troughmember and the other set being arranged to discharge vapour laterally tothe distribution chamber on the other side of the outer trough member.17. A reactor according to claim 16, wherein the two sets of secondapertures are symmetrically positioned with respect to the axes of theouter trough member and of the quench gas conduit.
 18. A reactoraccording to claim 1, wherein the quench gas conduit or conduits of onediaphragm is or are radially offset about the axis of the reactor withrespect to the corresponding quench gas conduit or conduits of at leastone other diaphragm within the pressure vessel.
 19. A reactor accordingto claim 18, wherein the quench gas conduit or conduits of one diaphragmis or are radially offset about the axis of the reactor with respect tothe quench gas conduit or conduits of at least one other diaphragm by anangle of between 20° and 90°.
 20. A reactor according to claim 19,wherein the angle of radial offset is 90°.
 21. A reactor according toclaim 1, wherein the quench gas conduit associated with the or eachrespective pair of trough members is mounted at least partially withinthe inner trough member of the pair.
 22. A continuous process forconducting an exothermic vapour phase reaction, which process comprises:a) supplying to a pressure vessel via inlet means therefor a gaseousreactant or reactants; b) maintaining in the pressure vessel temperatureand pressure conditions effective for production of the desired productby means of the exothermic vapour phase reaction; c) allowing thegaseous reactant or reactants to flow in turn through a plurality ofbeds of a heterogeneous catalyst effective for catalysts of theexothermic vapour phase reaction, each bed being supported within thepressure vessel by a respective support means; d) collecting vaporousreaction mixture exiting a first bed of each successive pair of beds ina vapour collection chamber disposed adjacent an exit end of said firstbed of the pair, the vapour collection chamber being separated from acorresponding downstream vapour redistribution chamber disposed adjacentan inlet end of the other bed of the pair and arranged forredistributing vapour over the inlet end of said other bed of therespective pair by a diaphragm extending across the interior of thepressure vessel, the diaphragm preventing the flow of vapour from thevapour collection chamber to the vapour redistribution chamber; e)allowing vaporous reaction mixture to pass from the vapour collectionchamber to the vapour redistribution chamber by means of a tortuouspassageway formed by at least one pair of nested trough memberscomprising an inner trough member and an outer trough member associatedwith and extending at least partially across the diaphragm, the innertrough member opening to the vapour collection chamber and having one ormore first apertures along the length of the inner trough member and theouter trough member communicating laterally on each side with the vapourredistribution chamber by means of one or more second apertures openinglaterally of the outer trough member into the vapour redistributionchamber along a respective side thereof, the space between the innertrough member and the outer trough member providing said tortuouspassageway for vapour from the vapour collection chamber to the vapourredistribution chamber through the at least one first aperture, throughthe space between the inner trough member and the outer trough member,and then through the at least one second aperture to discharge laterallyinto the vapour redistribution chamber; f) supplying quench gas to thevaporous reaction mixture passing through the diaphragm by means of aquench gas conduit associated with each pair of inner and outer troughmembers, the quench gas conduit being provided with one or more thirdapertures along its length arranged to discharge quench gas into thevapour flowing along the tortuous pathway; and g) recovering from thepressure vessel via outlet means provided downstream from the finalcatalyst bed a vaporous product stream containing said product, wherebythe diaphragm prevents passage of vapour from the vapour collectionchamber to the vapour redistribution chamber and whereby vapour passesfrom the vapour collection chamber to the vapour redistribution chamberthrough the tortuous passageway and is admixed with quench gas inpassage through the tortuous passageway.
 23. A process according toclaim 22 including providing adjacent the diaphragm a baffle meansextending across the interior of the pressure vessel and having at leastone breach through which the vaporous reaction mixture is constrained topass.